Non-linear optical switch

An optical switch is provided that utilizes a signal light frequency shift due to the resonance excitation non-linear optical effect in a semiconductor material so that a high extinction ratio optical switching operation can be realized with low energy controlling light pulses. The non-linear optical waveguide 1 receives a signal light pulse of a frequency of .omega.1 and a controlling light pulse of a frequency of .omega.0 and sets the pulse width of the controlling light pulse to a value smaller than that of the signal light pulse. The optical waveguide portion of the non-linear optical waveguide 1 is formed of a non-linear optical medium of which the non-linear refractive index changes due to absorption or amplification of the controlling light. The frequency .omega.1 of the signal light is set to the transparent region of the non-linear optical waveguide 1. When the frequency .omega.0 of the controlling light is set to the absorption region of the non-linear optical waveguide 1, some of signal light pulses incident together with the controlling lights partially frequency-shift toward the high-frequency area. The optical frequency filter 2 outputs only the frequency-shifted components. This allows the optical switching operation to be realized by controlling light pulses with low energies.